Well, I think 10% is a little unrealistic... it would mean your motor is 10x the size it needed to be.
11bgrunt
What the Utility is referring to is that with a Soft Starter, the motor is highly unlikely to be able to accelerate without the current getting to AT LEAST 200% of motor FLA, and then only if the motor can start uncoupled (i.e. a clutch system of some sort). For pumps and fans it usually 300-350% minimum (open flow), for anything else it could be a lot more than that. this is because with a soft starter, you cannot accelerate over an unlimited amount of time, because the motor is heating up since the frequency is fixed and 60Hz, only the voltage is limited, so the motor operates at high slip at first. A VFD on the other hand can be programmed to take 1 minute, 10 minutes, 10 hours or, 1 year to accelerate if that's what it takes to keep the current low. Only a VFD can give you 100% torque at 100% FLA.
The down side of a VFD is that it is a very expensive soft starter if you have no need to change the speed of the machine. SOMETIMES it is what you need to do, it's just a hard pill to swallow. I once had to use a VFD to start some 2500HP gas compressors, even though they had no need to vary the speed. But even with soft starters, they were going to dim the lights in the nearby town, VFDs were the only solution that would work. Set it for Current Limit at 100% FLA, it took 12 minutes to accelerate to full speed, but it worked.